The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

The government was claiming Victoria's population fell by 11,000 last year, while ABS shows the state swelled by 75,000 people.

Mr Wells said he will seek the data and methodology used to calculate the funding cut to Victoria from Commonwealth Treasury officials.

"It is disappointing that you, as federal treasurer, would now effectively threaten to withhold future health payments to Victorian hospitals because the state has simply pointed out the implications of Federal funding cuts," Mr Wells said in the letter.

At Royal Melbourne Hospital, up to 700 patients will be forced to wait longer for elective surgery because of the funding cuts.

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State Health Minister David Davis has written to Victoria's 86 health bosses urging them to plan for the Commonwealth's mid-financial-year cuts.

He said the Commonwealth's revised funding arrangement is unprecedented and based on false population figures.

The arrangement will cut $15 million from Victorian hospitals in December alone, Reserve Bank of Australia figures show.

Mr Davis wrote to his federal counterpart Tanya Plibersek and said that bringing the cuts in halfway through the financial year made it difficult for hospitals - which planned their annual budgets in May - to adjust.

"These cuts are unprecedented ... this is no way for the commonwealth to run healthcare in this country," he told reporters in Melbourne on Tuesday.

"We're obviously very angry with the Commonwealth, hospitals are angry ... and the Commonwealth could still reverse this very unfortunate cut."

"It will be hundreds of beds and it will indeed be thousands of patients that are impacted."

Ms Plibersek says the state is trying to cover its mismanagement.

"This is a smokescreen for the Victorian government's own failures," she said.

"Before any of this was in discussion, there were record high numbers of people on Victorian elective surgery waiting lists."